Your multiple developer connections are limited only by the number of licenses installed on the development server. (Two are intially included with 4D Team Developer Professional.)

For each 4D Team Developer Expansion license, an additional developer can connect to your development server for data access, manipulation, design, and administration. An additional developer can connect to your development server for data access, manipulation, design and administration or to connect via 4D Mobile.

Licenses are applied on a concurrent connection basis: If you have five licenses and a team of eight developers, any five of those developers may be connected at a given time.